The present invention relates to a system for controlling supercharging pressure in an automotive engine having a turbocharger, and more particularly to a system for electronically controlling the operation of a wastegate valve.
In an automotive engine having a turbocharger, the wastegate valve is provided in a bypass around a turbine of the turbocharger so as to divert exhaust gas away from the turbine so that the supercharging pressure is kept substantially constant to prevent knocking of the engine. The wastegate valve is generally controlled by a feedback control system in accordance with a desired valve.
Japanese Patent Application Laid-Open 61-55316 discloses a feedback control system wherein the difference between an actual supercharging pressure detected by a supercharging pressure sensor and a desired intake pressure is calculated and the supercharging pressure is controlled by a PI control dependent on the calculated difference.
However, when the vehicle is rapidly accelerated, the control operation of the wastegate valve delayed with respect to the opening speed of the throttle valve of the vehicle, which causes extremely high supercharging pressure because of the overshooting of the control.
If a feedforward control is employed, such an overshooting can be reduced. However, the feedforward control can not satisfactorily control the supercharging pressure to a desired value. Therefore, it is preferable to correct the deviation of the controlled supercharging pressure from the desired value with the feedback control. However, if both the controls are effected at the same time, overshoot values in a transient state are added which excessively increases the supercharging pressure.